Electric vehicles and electric-hybrid vehicles are gaining in popularity with consumers. The electric motors in these vehicles are typically powered from multiple storage batteries disposed in a battery pack in the vehicle. If the battery pack needs to be recharged while the vehicle is parked, a wired coupling device is connected to the vehicle, typically by the vehicle operator. However, some operators object to having to ‘plug-in’ their vehicle each time the vehicle needs to be charged. Portable personal electronics, such as cellular telephones and tablet computers, are also powered by batteries that need to be recharged. Owners of these products also have similar objections to plugging in the device when charging is required.
Wireless or connector-less power transfer systems have been proposed. An example of a wireless power transfer system 10 for an electric or hybrid electric vehicle 12 is shown in FIG. 1A and includes a source resonator 14 lying on a parking surface 16 under the vehicle 12 being charged, and a corresponding capture resonator 18 mounted on the underside of the vehicle 12. The source resonator 14 is connected to an alternating electrical power supply 20 that generates a magnetic field 22 that wirelessly induces an electric current in the capture resonator 18 that is rectified and supplied to a battery pack 24 in the vehicle. Other applications of this technology may be used for lower power charging, such as charging portable personal electronics. As shown in FIG. 1B, the portable electronic device 25 includes a capture resonator (not shown) that is placed in a magnetic field (not shown) generated by a source resonator (not shown) contained within a charging mat 27 embedded in the central console 29 of a vehicle when the electronic device 25 is placed on or near the charging mat 27.
To achieve desired impedance matching of the source resonator 14 and the capture resonator 18, a matching network of passive electrical components (resistors, inductors, capacitors) is used. FIG. 2 an example of a matching network 26A and 26B that includes reactive components (inductors, capacitors) in any series/shunt topology and an impedance (hereinafter referred to as a “series Z”) connected in series to either the source resonator, the capture resonator or both. The series Z of matching network 26A, 26B or both, may be configured as a combination of reactive components to achieve a desired electrical impedance (hereinafter referred to as a “bank”). As illustrated in FIG. 3, the series Z can be implemented as a single bank 28 of components connected in series with one or the other terminal of the source resonator 14 or the capture resonator 18. Alternatively, as shown in FIGS. 4 and 5, the series Z may be configured as two banks 30, 32 of components, one bank connected in series with each terminal of the source resonator or the capture resonator. The sum of the impedance of both banks 30, 32 is equal to Z, e.g. the impedance of each bank may be Z/2. It is understood that for higher frequencies (typically greater than 10 MHz), but in many cases much lower, parasitic properties of the components in each bank and the resonator itself will require adjusting the value of components in each bank of FIG. 3. and FIG. 4. typically by as much as ±10% (hereinafter referred to as “tuning”).
A single bank 28 implementation of series Z matching network 26 provides low cost and relatively easy tuning process, but produces an unbalanced circuit topology, thus increasing common mode noise and electromagnetic interference (EMI) in the system 10. This may require the use of more expensive components elsewhere in the system 10 in order to suppress the common mode noise and/or additional filtration to reduce EMI.
A two bank 30, 32 implementation of series Z matching network 26 produces a balanced circuit topology that provides reduced common mode noise and EMI compared to an equivalent single bank 28 series Z matching network 26. However, using two banks requires at least doubling the number of components used to construct the two banks 30.32 compared to the single bank 28 matching network implementation of series Z, thus increasing component cost. The two bank matching network also increases process cost due to additional tuning complexity and an additional assembly step.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches to solving a problem, which in and of themselves may also be inventions.